High Energy Density Solid‐State Lithium Metal Batteries Enabled by In Situ Polymerized Integrated Ultrathin Solid Electrolyte/Cathode

Abstract Solid‐state batteries (SSBs) are regarded as the most promising next‐generation energy storage devices due to their potential to achieve higher safety performance and energy density. However, the troubles in the preparation of ultrathin solid‐state electrolytes (SEs) as well as the resultant compromise in mechanical strength greatly limit the safety application of SSBs. Herein, a novel in situ polymerized integrated ultrathin SE/cathode design is developed. The ultrathin ceramic layer supported on the cathode serves not only as a rigid scaffold to prevent direct contact between the cathode and anode but also as active inorganic fillers to enhance the mechanical properties of in situ polymerized SE film. The unique Li‐ion coordination environments as well as the Li hopping mechanism profoundly promote fast ion transport in composite SEs. The in situ polymerized SEs simultaneously achieve the balance in ultrathin thickness (10 µm), fast ion transport (0.65 mS cm −1 ), superior Young's modulus (66.8 GPa), and excellent interface contact. The pouch cells with practical Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 configuration achieve an ultrahigh volumetric energy density of 1018 Wh L −1 and safety performance. The in situ polymerized integrated ultrathin SE/cathode design exhibits great promise for the practical application of SSBs with high energy density and safety performance.